The present invention relates to pressure switches of the type employed in fluid pressure actuated devices and particularly hydraulically actuated devices such as automatic power transmissions for motor vehicles.
In motor vehicle automatic power transmissions, it is desirable to provide electronically controlled shifting for the speed changes and where hydraulic actuators are employed for effecting movement of the clutches, it is necessary to provide an electrical signal to the controller when the hydraulic pressure in the shifting circuits reaches a predetermined level. Accordingly, it has been the practice to provide pressure switches in the hydraulic shifting circuits to close an electrical circuit to provide an electrical signal to the controller of the hydraulic fluid pressure in the particular actuator fluid circuit.
Known pressure switches for the aforesaid motor vehicle automatic power transmissions have suffered from the disadvantages of contact failure and erratic movement of the contact actuating mechanism in response to non-symmetric application of the fluid pressure forces to the switch actuator mechanism. This has been found particularly troublesome in pressure switches having an elastomeric diaphragm or boot covering the switch actuator piston mechanism; and, problems have been encountered in providing switch contacts which exhibited long service life and repeatable actuation points with respect to movement of the switch actuator in response to changes in the sensed hydraulic fluid pressure.
Asymmetric movement of the actuator mechanism in the known pressure switches resulting from fluid pressure acting on the diaphragm or membrane has resulted in improper contact making and breaking within the switch and erratic switch operation which effects the electronic control of the transmission shifting.
Thus, it has been desired to provide a way or means of designing and fabricating a pressure switch suitable for extended service life in a motor vehicle power transmission and which maintains its calibration over the vehicle service life and provides for long contact life within the switch.
The present invention provides a diaphragm or boot operated pressure switch particularly suitable for sensing hydraulic pressure in a motor vehicle power transmission and which employs a piston centrally contacting the diaphragm with annular electrode contacts within the switch which are contacted by an annular flange provided on the piston. A flexible electrical conductor, preferably a helical wire spring provides continuous connection between the piston and one of the stationary annular contacts. Each of the stationary annular contacts has an electrical terminal extending therefrom and which is preferably formed integrally therewith. In the preferred practice, the annular electrodes are imbedded in molded plastic body members.